This invention relates to a carbon analyzer, and more particularly to an apparatus for measuring both the total organic carbon (TOC) content of a sample in the form of aqueous solution and the carbon content of a solid sample.
For the purpose of providing a carbon detector for both samples in the form of an aqueous solution (herein after referred to as liquid samples) and solid samples, it has been known to modify a TOC analyzer with a carrier gas supplying unit, a sample injection unit, a combustion-oxidation reaction unit and a CO.sub.2 detector for measuring the total organic carbon content of an aqueous solution by adding thereto a solid sample supplying unit adapted to convert the carbon component of a solid sample into CO.sub.2 in a solid sample combustion-oxidation unit and to transport it to the aforementioned CO.sub.2 detector together with a carrier gas. Use is made, for example, of a non-dispersive infrared (NDIR) gas analyzer as the CO.sub.2 detector. In other words, the measuring cell of this NDIR analyzer is used in common for the measurement of gases in both flow routes for liquid and solid samples.
In the case of a liquid sample, TOC measurements in the range of several ppm to several 100 ppm are of principal importance, and several 10 .mu.l (or several 10 mg) of the sample is usually used. It is difficult, however, to inject a large amount of such a sample into a combustion-oxidation reaction tube at high temperature because its water component is suddenly vaporized and increases its volume. On the other hand, the carbon content of solid samples is much higher, ranging between several 1000 ppm to several %. The weight of a solid sample can be easily measured by a balance, and it is preferable to make use of several 10--several 100 mg of a sample in order to prevent uneven carbon concentration. This means that about 100 times more CO.sub.2 is generated from a solid sample than from a liquid sample.
Since most carbon analyzers are designed primarily for samples in the form of aqueous solution, the NDIR measuring cells are also designed primarily for samples in the form of aqueous solution. If such a measuring cell is used for the measurement of a solid sample, either the measurement can be done only for a lower concentration of carbon or only a small amount of the sample can be used.
It is therefore an object of the present invention to provide a carbon analyzer capable of measuring the carbon content of both aqueous solutions and solid samples under appropriate conditions.
It is another object of the invention to provide a carbon analyzer capable of varying sensitivity of measurements when there is a change in the carbon concentration in the sample or the amount of the sample changes.